Multi-service transport apparatus with switch for integrated transport networks

ABSTRACT

A multi-service transport apparatus for integrated transport networks that may have an electrical matrix, termination function means handling signals incoming at said apparatus input, a plurality of termination function means interfacing different layers, and adaptation function means. The termination function means handling incoming signals are implemented in input/output port devices; the termination function means interfacing different layers and said adaptation function means are implemented in adapter devices. The matrix performs exclusively the switching of the incoming signals that are already terminated and adapted by said input/output port devices and by said adapter devices and it is transparent with respect to the signal format. The switch may have a time division multiplexing matrix provided with a number of matrix inputs and a number of matrix outputs; source address generators, connected to matrix outputs of the time division multiplexing matrix.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/190,811, filed Jul. 28, 2005 and U.S. patent application Ser. No.11/366,426, filed Mar. 3, 2006.

This application is based on, and claims the benefit of U.S. patentapplication Ser. No. 11/190,811, filed Jul. 28, 2005, which isincorporated by reference herein and which is based on, and claims thebenefit of European Patent Application No. 04 292 277.3 filed on Sep.22, 2004, which is incorporated by reference herein.

This application is based on, and claims the benefit of U.S. patentapplication Ser. No. 11/366,426, filed Mar. 3, 2006, which isincorporated by reference herein and which is based on, and claims thebenefit of European Patent Application No. 05 290 508.0 filed on Mar. 4,2005, which is incorporated by reference herein.

TECHNICAL FIELD

The present method and apparatus relates to the field oftelecommunications and, in particular, to the field of network elements.Even more in particular, the present method and apparatus relates to amulti-service transport apparatus suitable for handling signals comingfrom an integrated transport network.

The present method and apparatus also relates to the field of switchesfor telecommunication networks. More particularly, the present methodand apparatus relates to a switch for integrated telecommunicationnetworks, which is adapted to switch both TDM flows and packets. Thepresent method and apparatus further relates to a method for switchingboth TDM flows and packets.

BACKGROUND

Transmission networks can be classified according to their geographicalextension, their topology and the transmission protocol they use fortransmitting information.

In particular, according to the geographical extension it is possible toidentify, for instance, two types of transmission network:

Local Area Network (LAN), where network nodes are rather close to eachother, for example inside the same building or group of buildings; and

Wide Area Network (WAN), used for interconnecting LANs that are far fromeach others.

From the topological point of view, LANs have usually a bus or ringconfiguration, while WANs may have nodes arranged according to a mesh, abus or a ring configuration.

With regard to the transmission protocol, networks may be distinguishedin circuit switched networks and packet switched networks. In circuitswitched networks, information is transported from a source node to adestination node by a continuous stream of digital signals propagatingthrough the network at a constant rate; the stream is organized in asequence of frames with fixed length and format. Informationtransmission starts only when a “circuit” (namely, a routeinterconnecting the source node to the destination node) has beenestablished in the network. The circuit is used to transmit the wholestream of digital signals. SDH/Sonet synchronous protocol and PDHasynchronous protocol are examples of circuit switched networkstandards.

In contrast, in a packet switched network the information is exchangedin bursts called “packets”. Each packet includes the address of itsdestination node and is individually transmitted through the network.Each packet is routed node by node according to the traffic conditions;at the destination node, the correct packet sequence is reconstructed torecover the information. Packet length may vary depending on theinformation type (voice, data or video) and on network features (bitrate, network extension). Ethernet and Resilient Packet Ring (RPR) areexamples of packet switched network standards.

Nowadays, there exist integrated transport networks, i.e. networkscomprising different LANs interconnected by backbones, where LANs mayprovide different services, each service being supported by a differentnetwork standard, either circuit switched or packet switched. Forinstance, a single integrated transport network may include LANsproviding both Ethernet- and ATM-supported services; in turn, datarelated to these services may be mapped, for example, according to theSDH/Sonet standard and may be transported along the network backbonesaccording to that standard.

In an integrated transport network, each standard, which is supported bythe network, may be represented by a different network layer. Each layerN is interfaced with the two adjacent layers N+1 and N−1. Layer N+1 isClient of layer N, while layer N−1 is Server of layer N. In other words,a signal according to layer N+1 can be suitably mapped and transportedin a signal structure according to layer N. In turn, the signalstructure according to layer N can be suitably mapped and transportedinto a signal structure according to layer N−1.

For example, an integrated transport network comprising SDH and Ethernetsignals can be represented by a three-layer hierarchy, where Ethernet islayer #3, SDH-Lower Order is layer #2 and SDH-Higher Order is layer #1.In other words, Ethernet is Client of SDH-Lower Order, which is in turnClient of SDH-Higher Order.

The simultaneous presence of a plurality of network layers, i.e. of aplurality of network standards supported by the same integratedtransport network, requires multi-service transport apparatuses,suitable for handling all the signals coming from the integrated networkat each network layer. In particular, a multi-service transportapparatus should be able to carry out all of the signal processingfunctions, such as termination, adaptation and switching, according toeach network layer. For instance, a multi-service transport apparatusshould be able to extract a group of Ethernet packets from an incomingSDH-Higher Order frame, to perform a packet-switching operation on thepackets and finally either to transmit the packets over a LAN or to mapthe packets back in a SDH-Higher Order frame and to transmit the framethrough the backbone. Hence, a multi-service transport apparatuscomprises input/output ports, switch elements (such as TDM matrices orpacket matrices) and interfaces between layers. With such an equipment,the apparatus is able to interconnect each input of each network layerto each output of the same layer and of the other layers.

Different multi-service transport apparatuses are known in the art.These known apparatuses are based on different approaches, depending onthe integration level of the signal processing functions related todifferent layers: “multi network element” approach; and “single networkelement” approach.

The “multi network element” approach consists in assembling a pluralityof single-service shelves, each shelf comprising input/output ports andswitch elements, able to manage signals according to one single layer,and interfaces. Yet, such an approach is disadvantageous, since thepresence of one shelf for each of the supported layers impliesextra-costs, due to a non-optimized exploitation of each shelf and tothe management of different shelves, and an increase of the overalldimension of the apparatus.

Lower costs and dimensions can be obtained by a multi-service transportapparatus according to the “single network element” approach, whereprocessing functions related to different layers are integrated into asingle shelf. Three different multi-service apparatuses are known. Eachof them is based either on a TDM matrix, a packet matrix; or a TDMmatrix and a packet matrix.

In the first case, the multi-service apparatus comprises a main TDMmatrix (for example a matrix for SDH/Sonet switching) and a plurality ofsecondary packet matrices with smaller dimensions. Yet, this approachexhibits some disadvantages, such as a reduced scalability of the packettraffic.

In the second case, the apparatus is based on a main packet matrix andon a plurality of input/output ports, the ports comprising interfaces toconvert all the incoming traffic into packet-switchable signals. Thisapproach however, even though advantageous with respect to the previousone in terms of scalability, is a non-layered approach, i.e. it is notconsistent with the layered structure of the transport network. Thisprevents the implementation and the coexistence of some networkprotection mechanisms. Moreover, the interfaces included into theinput/output ports are very complex and expensive.

In the third case the apparatus comprises two main matrices, i.e. a TDMmatrix and a packet matrix, with input/output ports suitable to directthe incoming traffic on the matrices and means to interface the twomatrices. This approach is disadvantageous, since it implies extra-costsdue to the presence of the two matrices and of the additional functionsaimed to direct the traffic.

As already mentioned, intermediate nodes are responsible for routinginformation towards respective destination nodes. For instance,intermediate nodes may cross-connect, multiplex, regenerate or amplifyinformation.

In particular, nodes cross-connecting and/or multiplexing information,such as cross-connects and add-drop multiplexers, comprise switches. Aswitch is a device which is adapted to receive information through aplurality of input lines and selectively send the information to aplurality of output lines, according to the destination node of suchinformation.

In a packet-switched network, a switch (which is also termed packetswitch) switches each packet according to the content of its overhead.Typically, each input line of a packet switch is provided with a numberof buffers, which equals the number of output lines. Each packetincoming from a given input line is stored into the buffer correspondingto the output line indicated by the overhead content. In each buffer,packets are stored in a queue, where they wait to be taken by therespective output line. An output controller is provided for each set ofbuffers associated to a same output line. The output controller receivesfrom each buffer connected to it information about the state of thequeue (number of packets, packet sizes, etc.). According to theseinformation, each output controller instructs its respective output lineto take packets from the buffers associated thereto. The outputcontroller determines the order according to which packets must betaken, in order to avoid buffer saturation and switch congestion.

In a packet switch, switching is thus dynamically controlled, accordingto the overhead content of each incoming packet.

Besides, in synchronous circuit-switched networks, a switch (which istermed TDM switch) switches each tributary channel according to itsposition into the TDM flow.

A TDM switch comprises a TDM matrix, which is typically implemented as amemory. Each matrix input is adapted to write in predetermined portionsof the memory in predetermined time slots. Besides, each matrix outputis adapted to read from predetermined portions of the memory inpredetermined time slots. The predetermined time slots are estimated byrecovering the reference clock signal of the synchronous network, sothat writing and reading operations are synchronized.

Each TDM switch has a routing table indicating, for each matrix output,an ordered list of the tributary channels that must be taken by thematrix output. The routing table of a TDM switch is static, i.e. it ismodified only when changes in the channel configuration occur (e.g. oneor more tributary channels are switched on or switched off).

Each matrix output is provided with a source address generator. Thesource address generator of each matrix output generates, by processingthe information contained into the static routing table, an ordered listof source addresses. A source address is a memory address indicating theposition of the memory portions containing the tributary channel to betaken, as it will be described in greater detail herein after.

SUMMARY

Embodiments of the present method and apparatus may provide amulti-service transport apparatus for integrated transport networks,which overcomes the aforesaid problems of the prior art.

In particular, embodiments of the present method and apparatus mayprovide a multi-service transport apparatus for integrated transportnetworks able to carry out all the signal processing functions, such astermination, adaptation and switching, according to the standards forintegrated transport networks, the multi-service transport apparatusallowing interconnection between all the layers of the integratedtransport network without damaging its layered structure, and such thatall the cascaded protection schemes provided by the different layers canbe implemented.

Still embodiments of the present method and apparatus may provide amulti-service transport apparatus for integrated transport networks withno extra-costs due to the duplication of the devices and with anoptimized exploitation of the devices provided inside the multi-serviceapparatus.

Such embodiments are achieved, according to the present method andapparatus, by a multi-service transport apparatus according to claim 1.Further advantageous features of the present method and apparatus areset forth in the dependent claims. All the claims are deemed to be anintegral part of the present description.

The embodiments of the present method and apparatus may provide amulti-service apparatus for an integrated transport network, whichcomprises a plurality of signal layers. The apparatus comprises anelectrical matrix, termination function means handling signals incomingat apparatus inputs, a plurality of termination function meansinterfacing different layers, and adaptation function means. Thetermination function means handling incoming signals are implemented ininput/output port devices; furthermore, the termination function meansinterfacing different layers and the adaptation function means areimplemented in adapter devices. The matrix performs exclusively theswitching of the incoming signals that are already terminated andadapted by the input/output port devices and by the adapter devices andit is transparent with respect to signal format.

According to one embodiment, a separate adapter device is provided forat least one pair of termination and adaptation function means betweenadjacent layers. The adjacent layers could be: Ethernet layer & MultiProtocol Label Switching layer; Multi Protocol Label Switching layer &Resilient Packet Ring layer; Resilient Packet Ring layer & SDH LowerOrder layer; SDH Lower Order layer & SDH Higher Order layer; and SDHHigher Order layer & Optical Data Unit layer.

According to another embodiment, a separate adapter device is providedfor at least one pair of termination and adaptation function meansbetween non-adjacent layers. The non adjacent layers could be: MultiProtocol Label Switching layer & SDH Higher Order layer; Multi ProtocolLabel Switching layer & Optical Data Unit layer; Resilient Packet Ringlayer & SDH Higher Order layer; and Resilient Packet Ring layer &Optical Data Unit layer.

According to another embodiment, a separate adapter device is providedfor at least one pair of termination and adaptation function meansbetween adjacent layers and wherein a separate adapter device isprovided for at least one pair of termination and adaptation functionmeans between non-adjacent layers.

Preferably, at least one of the input/output port devices comprisespacket termination function means. Preferably, there is also a firstbackpanel driver for transmitting terminated packet signals to thematrix for performing packet layer switching.

Preferably, the apparatus further comprises a selector, the selectorreceives packet signals and outputs the received packet signals eitherto the packet termination function means or to a plug-in module which isapt to adapt the packet signals into time division multiplex signals andterminate the packet signals on time division multiplex layer.

Typically, the plug-in module comprises: Lower Order Path Terminationmeans, Higher Order Path Termination means; and Optical Data Unittermination means.

The first backpanel driver transmits signals from the plug-in module tothe matrix for performing time division multiplex layer switching.

Preferably, the packet termination function means, the selector and theplug-in module are arranged on a first board.

In the apparatus according to the present method and apparatus, at leastone of the input/output port devices comprises TDM termination functionmeans and processing means. Furthermore, the apparatus comprises asecond backpanel driver for transmitting the terminated/processed TDMsignals to the matrix for performing TDM layer switching. Preferably,the TDM termination function means and the processing means are arrangedon a second board.

The apparatus further comprises a Higher Order Adaptation boardreceiving Lower Order TDM signals and outputting higher order TDMsignals, the Higher Order Adaptation board in turn comprising an adapterdevice comprising adaptation function means and termination functionmeans.

A peculiar characteristic of the present method and apparatus is thatthe electrical matrix has a total switching capacity, which could beshared by different layer signals.

In a preferred embodiment, the apparatus comprises an optical switchdevice transparent with respect to incoming optical signal format. Theoptical switch device has a total optical switching capacity, whichcould be shared by different layer signals.

Hence, in a multi-service transport apparatus according to the presentmethod and apparatus, the switching function, performed by a switchdevice (matrix), is substantially separated from the termination andadaptation functions. In other words, the switch device is transparentto the format of the incoming signals, as signals at the input of theswitch device are already terminated and adapted by the input/outputport device and by the adapter device. Accordingly, the switch device isable to switch signals coming from different network layers; no moremultiple switch elements (TDM or packet matrices) are required toperform switching on different layers.

The hierarchical layered structure of the network, managed by theadapter devices, is then preserved.

Moreover, the traffic throughput corresponding to each layer can beeasily scaled by equipping a proper number of input/output port devicesand of adapter devices.

Further, according to the type of input/output port device connected tothe switch device, it is possible to share the overall trafficthroughput offered by the switch device among the different layers,according to the traffic throughput required by each layer.

Furthermore, embodiments of the present method and apparatus may providea switch for integrated telecommunication networks which is able toswitch both TDM flows and packets by means of a single switching matrixand wherein the exploitation of the switch resources is optimized andindependent from the ratio between TDM flow capacity and packetcapacity.

Embodiments of the present method and apparatus may also provide aswitch for integrated telecommunication networks wherein TDM flows andpackets undergo a fixed delay.

Embodiments of the present method and apparatus may further provide aswitch for integrated telecommunication networks wherein multicast andbroadcast transmission can be easily implemented, both for TDM flows andfor packets.

According to a first aspect, embodiments of the present method andapparatus may provide a switch for telecommunication networks comprisinga time division multiplexing matrix provided with a number of matrixinputs and a number of matrix outputs; and source address generatorsconnected to matrix outputs of the time division multiplexing matrix.The switch further comprises input modules, each of the input modulesbeing adapted to generate a fixed size block, the block comprising anumber of packets arranged according to a predefined order; matrix inputprocessing modules, each of the matrix input processing modules beingconnected to an input module to receive therefrom the fixed size block,and each of the matrix input processing modules being further connectedto a matrix input; and a dynamic provisioning module, which is adaptedto receive from the matrix input processing modules routing informationcomprised in the packets, generate, according to the routinginformation, a dynamic routing table, and supply the dynamic routingtable to the source address generators.

Preferably, it further comprises a static provisioning module which isadapted to supply a static routing table to the source addressgenerators.

According to one embodiment, the fixed size block further comprises aportion of time division multiplexing flow. In this case, the switchfurther comprises a clock module for recovering from the time divisionmultiplexing flow a reference clock signal, and supplying the referenceclock signal to source address generators.

Preferably, the routing information is sent to the dynamic provisioningmodule according to the predefined order.

According to one embodiment, the predefined order corresponds to theorder of matrix outputs to which packets are addressed.

Preferably, the switch is at least partially implemented in anapplication specific integrated circuit.

According to a second aspect, embodiments of the present method andapparatus may provide a method of switching information flows in atelecommunication network, the method comprising: generating fixed sizeblocks comprising a number of packets which are arranged according to apredefined order; taking routing information from the packets,generating, according to the routing information, a dynamic routingtable; generating source addresses according to the dynamic routingtable; and supplying the source addresses to matrix outputs of a timedivision multiplexing matrix.

The source addresses are preferably generated according to a staticprovisioning table.

According to one embodiment, the fixed size blocks are generated with aportion of a time division multiplexing flow.

The method preferably comprises: recovering a reference clock signalfrom the time division multiplexing flow; and timing the step ofgenerating source addresses according to the reference clock signal.

The step of taking routing information preferably comprises takingrouting information according to the predefined order.

A French patent application filed by the same Applicant of the presentapplication, which was filed before the present patent application, butpublished afterward, describes a switching system comprising inputmodules each connected to a switching matrix and to a correspondingcontroller. Each input module organizes packets that it receives intodigital data blocks with a fixed size, and makes transfers of theseblocks by successive cycles to the matrix. Each of these blocks isorganized into groups of digital data, these groups having correspondingmodifiable sizes and being stored according to a predetermined order andassociated with the corresponding output ports in the system. Each ofthese groups is formed of packets to be sent to a single correspondingoutput port. Any block transfer to the matrix is accompanied bytransmission of information representative of the corresponding sizes ofthe groups of the transferred block to the controller, and the groups ofeach transferred block are switched to their corresponding destinationoutput ports as a function of this information representing the sizes.

This French patent application neither describes nor suggests to providea switch for integrated networks for switching both TDM flows andpackets. Furthermore, this patent application neither describes norsuggests to dynamically generate, according to overhead of incomingpackets, source addresses of packets, thus using the source addresses tocontrol the matrix outputs of a TDM matrix for switching the packets.

On the contrary, according to the present method and apparatus, theinput modules arrange packets according to a predefined order; thematrix input processing modules drop the overheads of the packets intothe same predefined order, and send them to the dynamic provisioningmodule. The dynamic provisioning module processes the overheads andprovides a dynamic routing table, which allows the source addressgenerators to generate source addresses for the packets.

Thus, the switch according to the present method and apparatusadvantageously allows to avoid duplicating the resources of the switch,thus reducing the device cost.

Moreover, the switch according to the present method and apparatusadvantageously allows to optimize the exploitation of the switchresources, independently from the composition of the incoming trafficflow.

Besides, the switch according to the present method and apparatusadvantageously allows to easily implement multicast and broadcasttransmission, as the TDM matrix is controlled through its matrixoutputs.

Besides, the switch according to the present method and apparatusadvantageously allows to introduce a fixed delay both on TDM traffic andon packet traffic, as traffic management by means of queues is avoided.

Further features and advantages of the present method and apparatus willbecome clear by the following detailed description, given by way ofexample and not of limitation, to be read with reference to theaccompanying drawings.

DESCRIPTION OF THE DRAWINGS

The features of the embodiments of the present method and apparatus areset forth with particularity in the appended claims. These embodimentsmay best be understood by reference to the following description takenin conjunction with the accompanying drawings, and in which:

FIG. 1 schematically shows from a logical point of view a portion of amulti-service transport apparatus for an integrated transport networkcomprising at least three layers;

FIG. 2 schematically shows a known multi-service transport apparatusimplemented according to the “multi network element” approach;

FIG. 3 schematically shows a known multi-service transport apparatusimplemented according to the “single network element” approach, based ona TDM matrix;

FIG. 4 schematically shows a known multi-service transport apparatusimplemented according to the “single network element” approach, based ona packet matrix;

FIG. 5 schematically shows a known multi-service transport apparatusimplemented according to the “single network element” approach, based ona TDM matrix and a packet matrix;

FIG. 6 a schematically shows from a logical point of view a firstembodiment of a multi-service transport apparatus according to thepresent method and apparatus;

FIG. 6 b schematically shows from a logical point of view anotherembodiment of a multi-service transport apparatus according to thepresent method and apparatus;

FIG. 7 shows the electrical scheme of a further embodiment of amulti-service transport apparatus according to the present method andapparatus;

FIG. 8 schematically shows a known packet switch;

FIG. 9 schematically shows a known TDM switch;

FIG. 10 schematically shows a switch for integrated networks accordingto the present method and apparatus;

FIGS. 11 a and 11 b schematically show blocks as generated by an inputmodule according to the present method and apparatus;

FIG. 12 schematically shows an example of the method for switching TDMflows and packets according to the present method and apparatus; and

FIG. 13 shows an example of the method for switching TDM multicast flowsaccording to the present method and apparatus.

DETAILED DESCRIPTION

Embodiments of the present method and apparatus relate to the concept ofa multi-service node, which switches packet and TDM traffic both using asingle switch matrix that is transparent with respect to the signalformat. As mentioned above, an integrated transport network deals withdifferent transmission standards, either circuit switched or packetswitched. All the transmission standards supported by the network areorganized into a hierarchical layered structure. A multi-servicetransport apparatus for integrated transport network thus comprisesdevices to handle at each network layer all the signals incoming at theinput of the apparatus.

FIG. 1 schematically shows, from a logical point of view, a portion of amulti-service transport apparatus P for an integrated transport networkcomprising at least three layers N+1, N and N−1. Layer N+1 is Client oflayer N, which is in turn Client of layer N−1. In other words, layer N−1is Server of layer N, which is in turn server of layer N+1.

The apparatus P comprises, for each of the above-mentioned layers, aprocessing block P_(N+1), P_(N) and P_(N−1). Each block P_(N+1), P_(N)and P_(N−1) comprises:

an adaptation function sink (A_(N+1), A_(N) and A_(N−1)) from the Serverlayer;

an adaptation function source (A′_(N+1), A′_(N) and A′_(N−1)) to theServer layer;

an input termination function (T_(N+1), T_(N) and T_(N−1));

an output termination function (T′_(N+1), T′_(N) and T′_(N−1)); and

a switch element (M_(N+1), M_(N) and M_(N−1)) suitable to performswitching at each of the layers (e.g. TDM matrix or packet matrix).

It has to be noticed that the apparatus P comprises both termination andadaptation functions to handle signals coming at the input of each blockP_(N) from the network, and termination and adaptation functionssuitable to interface blocks of different layers. For clarity reasons,FIG. 1 shows only the termination and adaptation functions suitable tointerface blocks of adjacent layers.

A signal according to layer N which is incoming at the input of theapparatus P, is firstly received by suitable termination/adaptationfunctions (not shown in FIG. 1) of the block P_(N). The signal can thenbe switched at layer N by the switch element M_(N) and finally go out ofthe apparatus through suitable termination/adaptation functions (notshown in FIG. 1) of the block P_(N).

Alternatively, the signal according to layer N may be received bysuitable termination/adaptation functions (not shown in FIG. 1) of theblock P_(N), then it can be switched by the switch element M_(N) andfinally adapted by the adaptation function A′_(N) which, together withthe termination function T_(N−1), allows the signal to pass from theClient layer N to the Server layer N−1. Then, the signal may be switchedby the switch element M_(N−1), and finally go out of the apparatus P atlayer N−1 through suitable termination/adaptation functions (not shownin FIG. 1) of the block P_(N−1).

Alternatively, the signal according to layer N may be received bysuitable termination/adaptation functions (not shown in FIG. 1) of theblock P_(N), then it can be switched by the switch element M_(N) andfinally it can pass from the Server layer N to the Client layer N+1through the termination function T′_(N) and the adaptation functionA_(N+1). Then, the signal may be switched by the switch element M_(N+1)and finally go out of the apparatus P at layer N+1 through suitabletermination/adaptation functions (not shown in FIG. 1) of the blockP_(N+1).

On the basis of the above considerations, it is clear that in amulti-service apparatus of the type shown in FIG. 1 each input of layerN is interconnected to all the output of layer N and of layers N−1 andN+1. Moreover, in such a multi-service apparatus, it is possible toperform switching according to each layer on all the incoming signalsaccording to all the three layers, thanks to the termination andadaptation functions allowing the signal to pass from each layer to theothers.

FIG. 2 schematically shows a known multi-service transport apparatusimplemented according to the “multi network element” approach. Accordingto this approach, the apparatus P is obtained by assembling a number ofshelves, each shelf comprising the processing functions according to onesingle layer.

In particular, the multi-service apparatus P shown in FIG. 2 comprisestwo shelves S₁ and S₂. The first shelf S₁ comprise all the processingfunctions according to the SDH/Sonet server layer of the network; thesecond shelf S₂ includes all the processing functions according to theEthernet Client layer of the network. S₁ is then substantially anSDH/Sonet Add-Drop Multiplexer (SDH/Sonet ADM), while S₂ issubstantially an Ethernet Switch.

Hence, the multi-service apparatus P shown in FIG. 2 allows to receiveat its input either a TDM signal STM-N^(input) from the SDH/Sonet layer,or packet signals Eth^(input), FE^(input), GE^(input), 10 GE^(input)from the Ethernet layer (respectively in its known formats Ethernet,Fast Ethernet, Gigabit Ethernet, 10 Gigabit Ethernet). Each of thesesignals can be either switched at its own layer, or pass to the otherlayer and then be switched.

The multi-service apparatus P shown in FIG. 2 suffers from somedisadvantages. First, a separate shelf is needed for each network layer,independently from the traffic throughput actually required by eachlayer. Referring to FIG. 2, for instance, it is assumed that thethroughput offered by the SDH/Sonet ADM is completely used, while only afraction of the throughput offered by the Ethernet Switch is actuallyexploited. It is also assumed that a further increase of the SDH/Sonettraffic throughput occurs. In the apparatus P shown in FIG. 2, theincrease of traffic throughput for SDH/Sonet traffic can be achievedonly by replacing the SDH/Sonet ADM with a similar device with increasedthroughput, but it is not possible to exploit the unemployed capacityoffered by the Ethernet Switch. Hence, with a “multi network element”approach the exploitation of the devices already provided inside theapparatus P is not optimized. In addition, having a plurality ofindependent shelves results in additional costs due to the management ofeach separate shelf and excessive apparatus dimensions.

FIG. 3 schematically shows a multi-service transport apparatus Paccording to a known “single network element” approach based on a TDMmatrix. The apparatus P shown in FIG. 3 comprises:

a main TDM matrix M_(TDM);

an input and output Optical Add-Drop Multiplexer (OADM^(in) andOADM^(out) respectively) to add or drop signals according to the WDMlayer;

TDM input/output ports 30 and 31 comprise termination/adaptationfunctions of the signals entering the apparatus according to theSDH/Sonet layer. The TDM input/output ports 30 and 31 may additionallycomprise functions to convert signals coming from the WDM layer to aTDM-switchable format; and

data ports 32 which are appended to the matrix M_(TDM), comprisingtermination/adaptation functions of signals entering the apparatusaccording to the Ethernet layer and secondary packet matrices M_(P) toperform packet switching.

Advantageously, this approach fits the hierarchical layered structure ofthe network. Nevertheless, it exhibits a reduced scalability of thepacket traffic throughput. The packet traffic throughput, indeed,depends on the dimension of the packet matrices M_(P), so it can beincreased only by replacing the existing packet matrices M_(P) with asimilar device with increased throughput. On the contrary, increasingthe number of packet matrices M_(P) appended to the main TDM matrixM_(TDM) does not increase the packet traffic throughput, since thepacket matrices work in parallel. Moreover, the packet traffic mapped inSTM-N frames must always cross the M_(TDM) matrix, even if it has toundergo packet switching.

Further approaches for providing multi-service transport apparatus areknown; FIGS. 4 and 5 schematically show, respectively, a multi-servicetransport apparatus according to the known single network elementsapproach based on a packet matrix (FIG. 4), and on a TDM matrix & apacket matrix. (FIG. 5)

Referring to FIG. 4 the apparatus P includes a packet matrix and meansfor converting all the incoming traffic in packet-switchable signals.This way, all the switching functions are implemented by the packetmatrix.

In particular, the apparatus P includes:

a main packet matrix M_(P);

an input and an output Optical Add-Drop Multiplexer (OADM^(in) andOADM^(out), respectively) to add and drop signals according to the WDMlayer;

TDM input/output ports 30 and 31 including termination/adaptationfunctions of the signals entering the apparatus according to theSDH/Sonet layer. The ports 30 and 31 additionally comprise TDM/PacketAdaptation functions (TDM/P) and Packet/TDM Adaptation functions (P/TDM)to convert the SDH/Sonet signals in packet signals and vice-versa. Inparticular, the TDM/Packet Adaptation consists in splitting thecontinuous stream of incoming STM-N frames in cells, while thePacket/TDM Adaptation consists in assembling the cells to recover thesequence of STM-N frames. The TDM input/output ports 30 and 31 mayadditionally comprise functions to convert signals coming from the WDMlayer to a TDM-switchable format; and

data input/output ports 40 and 41 for termination/adaptation of signalsaccording to the Ethernet layer.

The main disadvantages of this approach are the cost of the TDM/PacketAdaptation and Packet/TDM Adaptation functions and the fact that thisapproach cannot maintain the hierarchical layered structure of thenetwork. Indeed, the TDM and packet switching functions collapse in asingle switching function performed by the packet matrix M_(P), i.e. thefunctional hierarchy of the layers is not preserved inside theapparatus. This prevents the implementation of the cascaded mechanism ofnetwork protection according to the different layers. Finally, theTDM/Packet Adaptation function may either introduce undesired delay onthe lower order traffic or lead to an under-utilization of the packetmatrix capacity.

FIG. 5 schematically shows a multi-service transport apparatuscomprising means to drive the incoming signals on one of the twomatrices. In particular, the apparatus P shown in FIG. 5 comprises:

a TDM matrix M_(TDM) and a packet matrix M_(P);

an input and an output Optical Add-Drop Multiplexer (OADM^(in) andOADM^(out), respectively) to add and drop signals according to the WDMlayer (Σλi^(input), Σλi^(output));

TDM input/output ports 30, 31 including termination/adaptation functionsof the signals entering the apparatus according to the SDH/Sonet layer.The TDM input/output ports 30, 31 may additionally comprise functions toconvert signals coming from the WDM layer to a TDM-switchable format;

data input/output ports 40, 41 for termination/adaptation of signalsaccording to the Ethernet layer; and

a TDM-packet adapter 50 between the two matrices M_(TDM) and M_(P).

This approach disadvantageously requires the duplication of the switchelements and extra costs due to the apparatus charged to drive theincoming signals on one of the two matrices. The apparatus according tothis approach actually requires an additional overhead for packettraffic over SDH/Sonet, so that this packet traffic can be driven to theTDM-packet adapter 50 and then to the packet matrix M_(P). Furtheradditional costs are due to the connection of each input of theapparatus P to both matrices.

FIG. 6 a shows from a logical point of view a first embodiment of amulti-service transport apparatus for integrated transport networksaccording to the present method and apparatus. The multi-serviceapparatus P shown in FIG. 6 a comprises a matrix M and a plurality oftermination functions 60, 60′ (represented in FIG. 6 a by triangles) andadaptation functions 61 (represented in FIG. 6 a by trapezoids). Only afew termination and adaptation functions 60, 60′, 61 have been indicatedfor clarity. The termination functions can be divided into terminationfunctions 60′ handling signals incoming at the input of the apparatus Pfrom the network, and termination functions 60 interfacing differentlayers, either adjacent or not adjacent.

According to the present method and apparatus, the termination functions60′ according to each network layer are implemented in input/output portdevices PD.

Moreover, according to the present method and apparatus, optionaltermination functions 60 and adaptation functions 61 interfacingdifferent layers are implemented in adapter devices AD. In FIG. 6 a, forclarity reasons, a single adapter device AD including a terminationfunction 60 and an adaptation function 61 is shown; however, a separateAD is provided for each pair of termination and adaptation functionsbetween different layers.

Each adapter device AD is independent and can thus be inserted into theapparatus in case of need, i.e. when two or more network layers must beinterfaced. Each adapter device may include termination and adaptationfunctions for interfacing two or more levels, adjacent or not. Forinstance, the multi-service apparatus P shown in FIG. 6 a, given by wayof example, comprises an adapter device for each pair of adjacentlayers, i.e. an adapter device for interfacing: Ethernet (L2)—MultiProtocol Label Switching (MPLS); MPLS—Resilient Packet Ring (RPR);RPR—SDH Lower Order (LPC); LPC—SDH Higher Order (HPC); and HPC—OpticalData Unit (ODU).

Additionally, the apparatus P shown in FIG. 6 a includes adapter devicessuitable to interface the MPLS—HPC layers and MPLS—ODU layers, bypassingthe RPR and the LPC layers, and adapter devices suitable to interfaceRPR—HPC layers and RPR—ODU layers, bypassing the LPC layer. Yet, othercombinations of interfaced layers are possible.

The implementation of the termination and adaptation functions indedicated input/output port devices PD and adapter devices AD allows toimplement the switching functions according to all the network layersinto a single electric switch device or electric matrix M. The matrix Mperforms exclusively the switching of the incoming signals that arealready terminated and adapted by the input/output port devices and bythe adapter devices. Thus, the matrix M is able to switch signalsaccording to all the network layers, both circuit switched or packetswitched. In other words, the switch function is the same for all theincoming signals, both belonging to TDM traffic and to packet traffic.The switching function is transparent with respect to the signal format.

In FIG. 6 a, the matrix M is represented as a group of different switchelements or matrices with different logical function; in particular, inthe scheme in FIG. 6 a a separate logical function is highlighted foreach network layer: L2 switching for Ethernet layer; MPLS switching forMPLS layer; RPR switching for RPR layer; Lower Order Path Connection(LPC) for SDH-Lower Order; Higher Order Path Connection (HPC) forSDH-Higher Order; and ODU switching for ODU layer.

However, this subdivision is merely logical, and not physical. Thanks tothe implementation of termination and adaptation functions in separatedevices, a physically single matrix M is able to switch with nodistinction signals according to different layers. The logical functionof each input of the matrix M depends exclusively on the type ofinput/output port device and/or adapter device connected to it. Thetraffic throughput of each network layer thus depends on the number ofinput/output port devices or of adapter devices equipped and connectedto the matrix M.

The multi-service apparatus P according to the present method andapparatus may optionally comprise optical switch devices, such as theones employed in the Optical Multiplex Section (OMS) layer and in theOptical Channel (Och) layer, as shown in FIG. 6 b. As for the case ofelectrical signal processing, also in case of optical signal processingthe termination and adaptation functions are implemented in dedicatedinput/output port devices and adapter devices, so that the two switchfunctions relating to the two optical layers may be implemented in asingle optical switch device, or optical matrix MO, transparent withrespect to the format of the optical signal.

The present method and apparatus results in a number of advantages.Firstly, the apparatus exhibits a hierarchical structure managed by theadapter devices and consistent with the hierarchical layered structureof an integrated transport network. It follows that an apparatusaccording to the present method and apparatus is compatible with theimplementation of network protection schemes according to the differentlayers.

Moreover, the implementation of termination and adaptation functions tointerface different layers in adapter cards allows to change thethroughput percentage of each single network layer of the overallthroughput offered by the matrix M, by simply changing the number ofinput/output port devices and adapter devices equipped and connected tothe matrix M.

Finally, the complexity and the cost of the interface functions betweendifferent layers is shared among physically separated elementary adapterdevices, which can be inserted one by one into the apparatus only incase of need. This way, the cost of the overall multi-service apparatusis actually proportional to the actual traffic throughput provided bythe multi-service apparatus.

FIG. 7 shows the electrical scheme of a further embodiment of amulti-service transport network according to the present method andapparatus. The multi-service apparatus P shown in FIG. 7 comprises:

a matrix board MB comprising an electrical matrix M;

an SDH board, i.e. an input/output port device comprisingtermination/adaptation functions to terminate and adapt STM-n framescoming from the SDH/Sonet layer; and

an L2 board, i.e. an input/output port device comprisingtermination/adaptation functions to terminate and adapt packets comingfrom the Ethernet layer.

Optionally, the apparatus P may include adapter devices to interface thedifferent layers. Apparatus P of FIG. 7, for instance, comprises twoadapter devices AD1 and AD2, differently implemented. The first adapterdevice AD1 consists in a Multi-Service Plug-In Module, i.e. a devicecomprising a plurality of termination and adaptation functions which, incase of need, can be plugged-in on a input/output port device. Forexample, in the apparatus of FIG. 7 the Multi-Service Plug-In Module isplugged-in on the L2 board, and it comprises termination and adaptationfunctions to interface Ethernet layer and SDH—Lower Order layer,Ethernet layer and SDH—Higher Order layer, and Ethernet layer andOptical Data Unit layer.

The second adapter device AD2 consists in a Higher Order Adaptationboard, i.e. in an adapter device comprising termination and adaptationfunctions to interface SDH Lower Order and SDH Higher Order layers,implemented on a dedicated board which, in case of need, can be insertedinto the apparatus P. The AD2 device can be individually inserted intothe apparatus by connecting its input/output directly to the matrixboard MB.

Hence, an Ethernet signal (e.g. E, GE or 10 GE) incoming at the input ofthe apparatus P enters the L2 board through the PHY (physicaltermination of electric layer 1); afterwards, the Ethernet signal maybe:

processed by the packet termination functions laying on the L2 board(Pkt proc, Traffic mng) and then, through the backpanel driver BKP1, betransmitted to the matrix board MB, where a portion of the matrixperforms packet switching; or

processed by the adaptation and termination functions laying on theadapter device AD1, which allow to convert the signal to a highernetwork layer, where it can be switched by another portion of the matrixM laying on the matrix board MB.

In this latter case, the Ethernet signal is directed to theMulti-Service Plug-In Module, where it is adapted by the L2 so-skadaptation function. Afterwards, the Ethernet signal may be terminatedaccording to the SDH—Lower Order layer by the Lower Order PathTermination function (LPT so-sk) and then be transmitted through thebackpanel driver BKP1 to the matrix board, where a portion of the matrixM performs SDH—Lower Order switching. The signal can be switched eitherto the output of the matrix board MB connected to input/output portdevices (not shown in FIG. 7), or to an output of the matrix board MBconnected to the adapter device AD2. The adapter device AD2 can adaptthe signal through the Higher Path Adaptation function (HPA sk-so) andterminate it according to the SDH—Higher Order layer through the HigherOrder Path Termination function (HPT so-sk). The signal can finally betransmitted to the matrix board MB through the backpanel driver BKP2,where another portion of the matrix M performs SDH—Higher Orderswitching.

Alternatively, the Ethernet signal at the input of the L2 board can bedirected to the Multi-Service Plug-In Module, where it is adapted by theL2 so-sk function and then directly terminated according to theSDH—Higher Order layer through the Higher Order Path Terminationfunction (HPT so-sk). Then, the signal can be sent through the backpaneldriver BKP1 to the matrix board MB, where a portion of the matrix Mperforms SDH—Higher Order switching.

Alternatively, the Ethernet signal at the input of the L2 board can bedirected to the Multi-Service Plug-In Module, where it is adapted by theL2 so-sk function and then directly terminated according to the OpticalData Unit layer through the Optical Data Unit termination function (ODUso-sk). Then, the signal can be sent through the backpanel driver BKP1to the matrix board MB, where a portion of the matrix performs ODUswitching.

At the input of the apparatus P shown in FIG. 7 it is also possible tohave STM-N frames according to the SDH/Sonet layer. The STM-N frames arereceived by the apparatus P through the SDH board, where they undergotermination though the Transport Terminal Function (TTF sk-so) andprocessing through an HVC block. Finally, the frames are sent viabackpanel driver BKP3 to the matrix board MB, where a further portion ofthe matrix M performs SDH Higher Order switching.

It is important to notice that all the aforesaid switching functions(packet switching, SDH—Lower Order switching, SDH—Higher Order switchingand ODU switching), performed by different portions of the matrix Mlaying on the matrix board MB, are actually the same switching function,as termination of signals according to different layers is implementedbefore entering the matrix board. Nevertheless, according to the formatof the terminated signals entering the matrix board through thebackpanel drivers of the input/output port devices and of the adapterdevices, this switching function corresponds to:

an L2 switching function in case of packet-terminated signals; or

a Lower Order Path Connection switching function (LPC) in case ofSDH—Lower Order terminated signals; or

a Higher Order Path Connection switching function (HPC) in case ofSDH—Higher Order terminated signals; or finally

an ODU switching function in case of ODU terminated signals.

In other words, each portion of the matrix M laying on the matrix boardMB is able to switch every type of incoming signal, according to thetype of input/output port device or adapter device connected to it.

The following describes an implementation of the concept of amulti-service node, which switches packet and TDM traffic both using asingle switch matrix that is transparent with respect to the signalformat. One example is a switch that is capable of switching packets andTDM forms in an integrated telecommunication network.

FIG. 8 schematically shows a known packet switch PS. The packet switchPS is connected to a number N of input lines Lin1, Lin2, . . . , LinN,and to a number M of output lines Lout1, . . . LoutM. The packet switchPS further comprises N.times.M buffers. More particularly, the firstinput line Lin1 is connected to M buffers B11 . . . B1M; the secondinput line Lin2 is connected to M buffers B21, . . . B2M; and theN.sup.th input line LinN is connected to M buffers BN1, . . . BNM. Thepacket switch PS further comprises M output controllers OC1, . . . OCM.In particular, the buffers B11, B21, . . . BN1 are connected the outputcontroller OC1; and the buffers B1M, B2M, . . . BNM are connected to theoutput controller OCM. Moreover, the buffers B11, B21, . . . BN1 areconnected to the output line Lout1, and the buffers B1M, B2M, . . . BNMare connected to the output line LoutM.

The operation of the packet switch PS, which has already been describedin the introduction of the present description, will be only brieflysummarized herein after.

A packet incoming through the input line Lin1 is stored in one of thebuffers B11, . . . B1M, according to the content of its overhead. Ineach buffer, packets are stored in a queue, waiting to be taken by thecorresponding output line Lout1, . . . . LoutM. The same considerationsapply also to the other input lines Lin2, . . . LinN.

The output controller OC1 associated to the output line Lout1 receivesfrom the buffers B11, B21, . . . BN1 information about the status of thequeue of each of buffers B11, B21, . . . BN1. According to theseinformation, the output controller OC1 determines the order according towhich packets into the buffers B11, B21, . . . BN1 must be taken by theoutput line Lout1. The same considerations apply also to the otheroutput lines Lout2, . . . LoutM.

FIG. 9 schematically shows a known TDM switch. The TDM switch TDMS isconnected to a number N of input lines Lin1, Lin2, . . . LinN and to anumber M of output lines Lout1, Lout2, . . . LoutM. The TDM switch TDMSfurther comprises a TDM matrix TDMM. The matrix TDMM may be implementedas a memory. Each matrix output is connected to a respective sourceaddress generator SAG1, SAG2, . . . SAGM. The switch TDMS furthercomprises a clock module CK, which is adapted to recover the referenceclock signal of the synchronous network and to provide it to the sourceaddress generators SAG1, SAG2, . . . SAGM. Besides, the source addressgenerators are connected to a static provisioning module SPM. The staticprovisioning module SPM is adapted to provide the source addressgenerators SAG1, SAG2, SAGM with a static routing table. As alreadymentioned, the static routing table indicates, for each matrix output,an ordered list of the tributary channels that must be taken. Accordingto the static routing table provided by the static provisioning moduleSPM, each source address generator SAG1, SAG2, . . . SAGM generates, forthe respective matrix output, an ordered list of source addressesindicating the memory position of the tributary channels that must betaken. Hence, each matrix output sends to the respective output line aTDM flow, which is composed by the taken tributary channels.

FIG. 10 schematically shows a switch for integrated telecommunicationnetworks according to the present method and apparatus. The switch forintegrated networks INS is connected to a number N of input lines Lin1,Lin2, . . . LinN and to a number M of output lines Lout1, Lout2, . . .LoutM. Each input line Lin1, Lin2, . . . LinN enters the switch INSthrough a respective input module IM1, IM2, . . . IMN. The switch INSfurther comprises a TDM matrix TDMM, having N matrix inputs and M matrixoutputs (not shown in FIG. 10). The matrix TDMM may be implemented as amemory. Each input module IM1, IM2, . . . IMN is connected to arespective matrix input through a respective matrix input processingmodule MIP1, MIP2, . . . MIPN. Each matrix output is provided with arespective source address generator SAG1′, SAG2′, . . . SAGM′. Theswitch INS further comprises a clock module CK, which is adapted torecover a reference clock signal of the synchronous network and toprovide it to the source address generators SAG1′, SAG2′, . . . SAGM′.Besides, each source address generator SAG1′, SAG2′, . . . SAGM′ isconnected to a static provisioning module SPM. The switch INS, accordingto the present method and apparatus, comprises also a dynamicprovisioning module DPM. Each matrix input processing module MIP1, MIP2,. . . MIPN is connected to the dynamic provisioning module DPM. Theoutput of the dynamic provisioning module DPM is connected to all thesource address generators SAG1′, SAG2′, . . . SAGM′.

It has to be noticed that typically the input modules IM1, IM2, . . .IMN are implemented on a port board PB, together with other port devices(not shown in FIG. 10). On the other hand, the TDM matrix, the matrixinput processing modules, the source address generators, the staticprovisioning module and the dynamic provisioning module are typicallyimplemented through one or more chips on a same matrix board MB, whichis separated from the port board PB. In another embodiment (not shown),only a single board is provided for input modules, TDM matrix, matrixinput processing modules, source address generators, static provisioningmodule and dynamic provisioning module, which may be implemented eitherthrough one or more chips. According to a preferred embodiment of thepresent method and apparatus, the memory implementing the TDM matrix isa data RAM memory, which is divided into two parts. While a first partis being written by the matrix inputs, a second part is being read bythe matrix outputs, and vice versa.

According to a preferred embodiment of the present method and apparatus,the memory is implemented as a number of memories working in parallel.This allows for a speed up of the reading functions performed by thematrix outputs.

According to a preferred embodiment of the present method and apparatus,the TDM matrix comprises a main matrix and a spare matrix, which issubstantially identical to the main matrix. Typically, incoming trafficis bridged both to the main matrix and to the spare matrix, which bothperform switching at the same time. Output ports (not shown) receiveoutput flows both from the main and spare matrices. During normaloperation, the output ports select the flows from the main matrix.Should the main matrix become failed, the output ports will select theflows from the spare matrix.

Herein after, by referring to FIGS. 10, 11 a and 11 b, a detaileddescription of the switch INS operation according to the present methodand apparatus will be provided.

According to the present method and apparatus, each input line Lin1,Lin2, . . . LinN of the switch INS is adapted to receive a respectiveinformation flow, which may comprise only TDM flows, packets or both TDMflows and packets. According to the present method and apparatus, eachinformation flow incoming at the switch INS through the input line Lin1,Lin2, . . . LinN, is divided by the respective input modules IM1, IM2, .. . IMN in blocks having fixed size. Additional processing functions ofthe input flows are performed by other port devices, which are notdescribed, as they are not relevant for the present description.

FIG. 11 a schematically shows the structure of an example of a blockgenerated by an input module. The fixed-size block FSB comprises apacket overhead field P-OH, a packet field PF and a TDM field TDMF. Thepacket field PF comprises a number k of packets P1, P2, . . . Pk. Suchpackets may have all the same size, or they can have different sizes,according to the protocol transporting them. The overall dimension ofthe packet field PF is thus variable, and it depends both on the numberk of packets and on the size of each packet. The packets P1, P2, . . .Pk are arranged into the packet field PF according to a predefinedorder. For instance, in a preferred embodiment of the method andapparatus, packets are arranged according to their respectivedestination output lines, as it will be shown in greater detail byreferring to FIG. 12.

The packet overhead field P-OH comprises the overheads of the packetsP1, P2, . . . Pk. Preferably, the overheads are arranged according tothe same predefined order as the packets. Thus, the packet overheadfield P-OH comprises the overhead OH 1 of the packet P1, the overheadOH2 of the packet P2 and the overhead OHk of the packet Pk.

Finally, the fixed-size block FSB may comprise a portion of a TDM flow.It has to be noticed that the TDM field may comprise different portionsTDM1, . . . TDMh of different TDM flows. For instance, the TDM field maycomprise portions of unicast TDM flows (e.g. SDH frame, Sonet frame),and/or portions of a multicast/broadcast TDM flow (e.g. a video signal).Switching of multicast/broadcast TDM flows will be described in detailwith reference to FIG. 13.

It must be noticed that the composition of each fixed size blockdynamically changes according to the composition of the traffic flow.For instance, one or more tributary channels of the TDM flow may beswitched off, or the transmission of a video signal may finish. In thesecases, the size of the TDM field decreases, and consequently the packetfield size and the packet overhead field size increase. This is shown inFIG. 11i b, which shows two consecutive blocks FSB1, FSB2 generated by asame input module according to the present method and apparatus. It canbe noticed that the size of the TDM field TDMF1 of the first block FSB1is larger than the size of the TDM field TDMF2 of the second block FSB2.Thus, in the block FSB2, a larger portion of the block is available forarranging packets and their overheads.

It has to be noticed that, if the incoming information flow comprisesonly packets, there is no TDM field into the block. Similarly, if theincoming information flow comprises only TDM flows, there are no packetoverhead field and packet field into the block, as it will be shownherein after, with reference to FIG. 13.

After each input module IM1, IM2, . . . IMN has generated a respectiveblock as shown in FIGS. 11 a and 11 b, each input module sends it to therespective matrix input processing module MIP1, MIP2, . . . MIPN. Eachmatrix input processing module MIP1, MIP2, . . . MIPN drops the packetoverhead field P-OH from the respective block, and sends it to thedynamic provisioning module DPM.

The dynamic provisioning module DPM, according to the content of thepacket overhead fields received from the matrix input processingmodules, generates a dynamic routing table. More specifically, thedynamic routing table may contain, for each matrix output:

the starting memory address of each packet that the matrix output has totake, and

the size of each packet that the matrix output has to take.

The dynamic provisioning module DPM sends such a dynamic routing tableto the source address generators SAG1′, SAG2′, . . . SAGM′. Furthermore,the source address generators SAG1′, SAG2′, . . . SAGM′ receive from thestatic provisioning module SPM a static routing table relative to theTDM portions. Therefore, by processing both the dynamic routing tableand the static routing table, each source address generator SAG1′,SAG2′, . . . SAGM′ generates, for its respective matrix output, anordered list of source addresses, i.e. an ordered list of memoryaddresses from where the matrix output may take packets and TDMportions.

Thus, according to the present method and apparatus, both TDM flows andpackets are switched by the same TDM matrix, which is controlled bymeans of the source address of the matrix outputs. Source addresses maybe generated either dynamically (for packets) or statically (forportions of TDM flows).

It has to be noticed that, advantageously, according to the presentmethod and apparatus, failures or down times of the main matrix can bemanaged in a substantially transparent manner. In fact, as switching isperformed by a TDM matrix, which is controlled by means of its outputs,and all the incoming traffic is bridged both to the main and to thespare matrixes, managing main matrix failures can be performed in a“hitless” manner, i.e. without loosing any portion of the incomingtraffic.

Besides, as already mentioned with reference to FIG. 11 b, thecomposition of a block may be different from the composition of thefollowing block. In particular, changes in TDM flows and/or in packetsresult in changes of the TDM field size and packet field size (seeblocks FSB1 and FSB2 of FIG. 11 b). As already mentioned, the memory isdivided into two parts. The two parts are able to store succeedingblocks. While a first part is being written by the matrix inputs, asecond part is being read by the matrix outputs, and vice versa. Forinstance, with reference to FIG. 11 b, while first block FSB1 is beingread from a first memory part, the second block FSB2 is being writteninto a second memory part. According to the present method andapparatus, in such a situation the dynamic routing table allows toupgrade in real time the packets source addresses, while a new staticrouting table must be provided in order to update the TDM portionssource addresses. In a preferred embodiment of the method and apparatus,a plurality of static routing tables may be provided to the sourceaddress generators, each routing table corresponding to a differentblock composition. For instance, by referring to FIG. 11 b, two staticrouting tables may be provided both for the block FSB1 and for the blockFSB2, respectively. In this way, a delayed provisioning of the newstatic routing table is avoided, and TDM portion source addresses can betransparently updated.

An example of the method for switching both TDM flows and packetsaccording to the present method and apparatus will be now described withreference to FIG. 12.

FIG. 12 shows a TDM matrix having four matrix inputs and four matrixoutputs. Each input module (not shown) provides the respective matrixinput processing module (not shown) with a fixed size block FSBin1,FSBin2, FSBin3, FSBin4. Each block comprises both a packet field, and aTDM field. More particularly, each block comprises four packets, eachpacket being addressed to a different destination matrix output, and anumber of TDM portions. In the following description, only packetswitching will be described in detail; on the contrary, a detaileddescription of the switching of the TDM flow can be found into thedescription of FIG. 9.

As mentioned above, according to the present method and apparatus, eachinput module arranges packets according to a predefined order. In FIG.12, packets are ordered according to their destination matrix outputs.In FIG. 12 each packet is marked with two indexes; a first indexindicates the matrix output the packet is addressed to (destinationmatrix output), while the second index indicates the matrix input thepacket comes from (source matrix input). Thus, the fixed size blockFSBin1 comprises packets P11, P21, P31 e P41. Similarly, the fixed sizeblock FSBin2 comprises packets P12, P22, P32 e P42. Similarly, the fixedsize block FSBin3 comprises packets P13, P23, P33 e P43. Finally, thefixed size block FSBin4 comprises packets P14, P24, P34 e P44. It has tobe noticed that, as already mentioned, packets have different sizes, sothat packet fields of the four blocks have different sizes.

Each block FSBin1, FSBin2, FSBin3, and FSBin4 further comprises a packetoverhead field, which in turn comprises the packet overheads arrangedaccording to the same predefined order of packets. Thus, the packetoverhead field of the block FSBin1 comprises the overhead OH11 of thepacket P11, the overhead OH21 of the packet P21, the overhead OH31 ofthe packet P31, and the overhead OH41 of the packet P41. Similarconsiderations apply also to blocks FSBin2, FSBin3 and FSBin4.

Each overhead may for instance comprise packet size, an identifier ofthe destination matrix output and an identifier of the source matrixinput. Thus, the overhead OHyx of a packet Pyx may be expressed as:

OHyx=(W _(yx) ,y,x),

wherein W_(yx), is the size of the packet Pyx, y is the identifier ofthe destination matrix output of the packet Pyx and x is the identifierof the source matrix input of the packet Pyx. It has to be noticed that,as the order according to which packets are arranged in a block ispredefined, the identifier of the destination matrix output and theidentifier of the source matrix input can be omitted. In this case, evenif a packet has size equal to 0, its overhead cannot be omitted, inorder to preserve the predefined order.

As already mentioned, a TDM matrix may be implemented as a memory. Whena TDM matrix switches TDM flows, matrix inputs are able to write atpredetermined memory addresses, while the matrix outputs are able toread from predetermined memory addresses. Similarly, the TDM matrix TDMMcomprised into the switch INS according to the present method andapparatus may be implemented as a memory. However, as the switch INSaccording to the method and apparatus is adapted to switch variable sizepackets, the memory positions wherein packets are stored dynamicallychange according to packet size.

FIG. 12 shows an example of a TDM matrix TDMM comprising atwo-dimensional memory MEM, i.e. a memory comprising a number of rowsand a number of columns. Thus, a memory address comprises a row addressand a column address.

Under the assumption that each matrix input writes the packets of therespective block one after the other into a respective row of the memoryMEM, the column addresses of the packets comprised in the block FSBin1are:

column address of packet P11: 0;

column address of packet P21: W₁₁;

column address of packet P31: W₁₁+W₂₁;

column address of packet P41: W₁₁+W₂₁+W₃₁; and

column address of the first TDM word: W₁₁+W₂₁+W₃₁+W₄₁.

Similarly, the column addresses of the packets comprised in the blockFSBin2 are:

column address of packet P12: 0;

column address of packet P22: W₁₂;

column address of packet P32: W₁₂+W₂₂;

column address of packet P42: W₁₂+W₂₂+W₃₂; and

column address of the first TDM word: W₁₂+W₂₂+W₃₂+W₄₂.

Similar considerations apply to blocks FSBin3 and FSBin4. Thus, eachmemory row comprises one after the other packets comprised in a block ofa respective matrix input, as shown in FIG. 12.

As each packet address dynamically varies with the size of all thepackets comprised into the block, the present method and apparatusprovides a dynamic provisioning module DPM. The dynamic provisioningmodule DPM processes the packet overhead field of each block, in orderto generate a dynamic routing table. As already mentioned, for eachmatrix output, the dynamic routing table comprises the starting addressof the packets that the matrix output has to take, and the size of eachpacket that the matrix output has to take.

For instance, for the first matrix output, the dynamic routing tableprovides:

for packet P11: row 0, column 0, size=W₁₁;

for packet P12: row 1, column 0, size=W₁₂;

for packet P13: row 2, column 0, size=W₁₃; and

for packet P14: row 3, column 0, size=W₁₄.

For the second matrix output, the dynamic routing table provides:

for packet P21: row 0, column W₁₁, size=W₂₁;

for packet P22: row 1, column W₁₂, size=W₂₂;

for packet P23: row 2, column W₁₃, size=W₂₃; and

for packet P24: row 3, column W₁₄, size=W₂₄.

For the third matrix output, the dynamic routing table provides:

for packet P31: row 0, column W₁₁+W₂₁, size=W₃₁;

for packet P32: row 1, column W₁₂+W₂₂, size=W₃₂;

for packet P33: row 2, column W₁₃+W₂₃, size=W₃₃; and

for packet P34: row 3, column W₁₄+W₂₄, size=W₃₄.

Finally, for the fourth matrix output, the dynamic routing tableprovides:

for packet P41: row 0, column W₁₁+W₂₁+W₃₁, size=W₄₁;

for packet P42: row 1, column W₁₂+W₂₂+W₃₂, size=W₄₂;

for packet P43: row 2, column W₁₃+W₂₃+W₃₃, size=W₄₃; and

for packet P44: row 3, column W₁₄+W₂₄+W₃₄, size=W₄₄.

The dynamic provisioning module DPM provides the dynamic routing tableto the source address generators. The source address generators,according to the information generate the source addresses, i.e. thememory addresses of each word of each packet.

Further, each source address generator is able to determine the startingaddress of the TDM portions. For instance, for the first row,corresponding to the first matrix input, the starting address of the TDMportion is given by the following formula:

$\begin{matrix}{\sum\limits_{y = 1}^{M}W_{y\; 1}} & (1)\end{matrix}$

Similar formulas can be applied for the other rows. Further, as eachblock has a fixed dimension, the formula (1) also allows the sourceaddress generators to determine the dimension of the TDM field TDMF.

Similarly, the source address generators are able, for each matrixoutput, to determine the starting address of the TDM portions. Moreparticularly, by estimating, for the first matrix output:

$\begin{matrix}{\sum\limits_{x = 1}^{N}W_{x\; 1}} & (2)\end{matrix}$

The source address generator of the first matrix output estimates theaddress wherein dynamic switching is replaced by static switching.Similar considerations also apply to the other matrix outputs.

It must be noticed that, for avoiding congestion of the TDM matrix, foreach matrix output the following condition must be fulfilled:

$\begin{matrix}{{\sum\limits_{x = 1}^{N}W_{y\; x}},{\leq C_{y}}} & (3)\end{matrix}$

wherein x is the matrix input identifier, y is the matrix outputidentifier, and C_(y) is the capacity of the matrix output y.

Besides, for avoiding congestion also the following condition must befulfilled for each matrix input:

$\begin{matrix}{{\sum\limits_{y = 1}^{M}W_{y\; x}},{\leq C_{x}}} & (4)\end{matrix}$

wherein C_(x) is the capacity of the matrix input x.

According to the present method and apparatus, congestion management isperformed by a suitable congestion management algorithm. The congestionmanagement algorithm determines, for each block, the maximum number ofpackets that the block may comprise and the maximum size of each packetcomprised into the block, in order to assure that the conditionsexpressed by (3) and (4) are fulfilled.

In a preferred embodiment of the present method and apparatus, thecongestion management algorithm is implemented on a dedicated device,which is generally termed central scheduler, which is not shown in FIGS.11 a and 11 b. This central scheduler, in a preferred embodiment of themethod and apparatus, is implemented on a chip, which is located on thematrix board.

FIG. 13 shows an example of the method for switching TDM multicast flowsaccording to the present method and apparatus. FIG. 13 shows a TDMmatrix TDMM having a number of matrix input; for simplicity, only amatrix input is shown in FIG. 13. Such a matrix input receives from thecorresponding input module (not shown in FIG. 13) a block FSBin, whichcomprises a packet overhead field P-OHin, a packet field PFin and a TDMfield. As already mentioned, a TDM field may comprise portions ofdifferent TDM flows. For instance, the TDM field of the block FSBincomprises a portion TDMu of a unicast flow (e.g. a portion of an SDH TDMflow). The TDM field of the block FSBin further comprises a portion TDMmof a multicast flow (e.g. a portion of a video signal). The TDM matrixof FIG. 13 is provided with four matrix outputs. It is assumed that theportion TDMm of multicast flow is addressed to the first, second andfourth matrix outputs (not to the third matrix output).

According to the present method and apparatus, the matrix input simplywrites the multicast flow portion TDMm into the memory MEM of the matrixTDMM as described by referring to FIG. 12. Thus, only a single copy ofthe portion TDMm is stored into the memory MEM, and each destinationmatrix output is simply required to read the copy of the portion TDMmfrom its source address. As it can be observed in FIG. 13, each of thefirst, second and fourth destination matrix outputs reads the portionTDMm from the memory MEM and inserts it into its respective output blockFSBout1, FSBout2, FSBout4. The position of the portion TDMm into eachoutput block depends both on static and on dynamic routing tables. Itcan be noticed, that, as already mentioned, no packet is addressed tothe matrix output 4. In this case, the whole fixed-size block FSBout4comprises TDM portions, and neither the packet field PF nor the packetoverhead field P-OH is included into the block.

Thus, according to the present method and apparatus, multicasting isimplemented by source address generators and by the matrix outputs,while matrix inputs and the memory are not required to create and store,respectively, a plurality of copies of the TDMm portion. This allowsreduces the processing complexity of multicasting and broadcastingtransmissions.

1. A multi-service apparatus for an integrated transport network whichcomprises a plurality of signal layers, said apparatus comprising anelectrical matrix, termination function means handling signals incomingat apparatus inputs, a plurality of termination function meansinterfacing different layers, and adaptation function means, whereinsaid termination function means handling incoming signals areimplemented in input/output port devices, further wherein saidtermination function means interfacing different layers and saidadaptation function means are implemented in adapter devices, furtherwherein said matrix performs exclusively the switching of the incomingsignals that are already terminated and adapted by said input/outputport devices and by said adapter devices and it is transparent withrespect to signal format.
 2. A switch for telecommunication networks,comprising: a time division multiplexing matrix provided with a numberof matrix inputs and a number of matrix outputs; source addressgenerators, connected to matrix outputs of the time divisionmultiplexing matrix; input modules, each of said input modules beingadapted to generate a fixed size block, said block comprising a numberof packets, arranged according to a predefined order; matrix inputprocessing modules, each of said matrix input processing modules beingconnected to an input module to receive therefrom said fixed size block,and each of said matrix input processing modules being further connectedto a matrix input; and a dynamic provisioning module, which is adaptedto receive from said matrix input processing modules routing informationcomprised in said packets, generate, according to said routinginformation, a dynamic routing table, and supply said dynamic routingtable to the source address generators.